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//===---- MipsOptimizeMathLibCalls.cpp - Optimize math lib calls. ----===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This pass does an IR transformation which enables the backend to emit native
// math instructions.
//
//===----------------------------------------------------------------------===//
#include "MipsTargetMachine.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/Intrinsics.h"
#include "llvm/Pass.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Target/TargetLibraryInfo.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
using namespace llvm;
static cl::opt<bool> DisableOpt("disable-mips-math-optimization",
cl::init(false),
cl::desc("MIPS: Disable math lib call "
"optimization."), cl::Hidden);
namespace {
class MipsOptimizeMathLibCalls : public FunctionPass {
public:
static char ID;
MipsOptimizeMathLibCalls(MipsTargetMachine &TM_) :
FunctionPass(ID), TM(TM_) {}
virtual const char *getPassName() const {
return "MIPS: Optimize calls to math library functions.";
}
virtual void getAnalysisUsage(AnalysisUsage &AU) const;
virtual bool runOnFunction(Function &F);
private:
/// Optimize calls to sqrt.
bool optimizeSQRT(CallInst *Call, Function *CalledFunc,
BasicBlock &CurrBB,
Function::iterator &BB);
const TargetMachine &TM;
};
char MipsOptimizeMathLibCalls::ID = 0;
}
FunctionPass *llvm::createMipsOptimizeMathLibCalls(MipsTargetMachine &TM) {
return new MipsOptimizeMathLibCalls(TM);
}
void MipsOptimizeMathLibCalls::getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<TargetLibraryInfo>();
FunctionPass::getAnalysisUsage(AU);
}
bool MipsOptimizeMathLibCalls::runOnFunction(Function &F) {
if (DisableOpt)
return false;
const MipsSubtarget &Subtarget = TM.getSubtarget<MipsSubtarget>();
if (Subtarget.inMips16Mode())
return false;
bool Changed = false;
Function::iterator CurrBB;
const TargetLibraryInfo *LibInfo = &getAnalysis<TargetLibraryInfo>();
for (Function::iterator BB = F.begin(), BE = F.end(); BB != BE;) {
CurrBB = BB++;
for (BasicBlock::iterator II = CurrBB->begin(), IE = CurrBB->end();
II != IE; ++II) {
CallInst *Call = dyn_cast<CallInst>(&*II);
Function *CalledFunc;
if (!Call || !(CalledFunc = Call->getCalledFunction()))
continue;
LibFunc::Func LibFunc;
Attribute A = CalledFunc->getAttributes()
.getAttribute(AttributeSet::FunctionIndex, "use-soft-float");
// Skip if function has "use-soft-float" attribute.
if ((A.isStringAttribute() && (A.getValueAsString() == "true")) ||
TM.Options.UseSoftFloat)
continue;
// Skip if function either has local linkage or is not a known library
// function.
if (CalledFunc->hasLocalLinkage() || !CalledFunc->hasName() ||
!LibInfo->getLibFunc(CalledFunc->getName(), LibFunc))
continue;
switch (LibFunc) {
case LibFunc::sqrtf:
case LibFunc::sqrt:
if (optimizeSQRT(Call, CalledFunc, *CurrBB, BB))
break;
continue;
default:
continue;
}
Changed = true;
break;
}
}
return Changed;
}
bool MipsOptimizeMathLibCalls::optimizeSQRT(CallInst *Call,
Function *CalledFunc,
BasicBlock &CurrBB,
Function::iterator &BB) {
// There is no need to change the IR, since backend will emit sqrt
// instruction if the call has already been marked read-only.
if (Call->onlyReadsMemory())
return false;
// Do the following transformation:
//
// (before)
// dst = sqrt(src)
//
// (after)
// v0 = sqrt_noreadmem(src) # native sqrt instruction.
// if (v0 is a NaN)
// v1 = sqrt(src) # library call.
// dst = phi(v0, v1)
//
// Move all instructions following Call to newly created block JoinBB.
// Create phi and replace all uses.
BasicBlock *JoinBB = llvm::SplitBlock(&CurrBB, Call->getNextNode(), this);
IRBuilder<> Builder(JoinBB, JoinBB->begin());
PHINode *Phi = Builder.CreatePHI(Call->getType(), 2);
Call->replaceAllUsesWith(Phi);
// Create basic block LibCallBB and insert a call to library function sqrt.
BasicBlock *LibCallBB = BasicBlock::Create(CurrBB.getContext(), "call.sqrt",
CurrBB.getParent(), JoinBB);
Builder.SetInsertPoint(LibCallBB);
Instruction *LibCall = Call->clone();
Builder.Insert(LibCall);
Builder.CreateBr(JoinBB);
// Add attribute "readnone" so that backend can use a native sqrt instruction
// for this call. Insert a FP compare instruction and a conditional branch
// at the end of CurrBB.
Call->addAttribute(AttributeSet::FunctionIndex, Attribute::ReadNone);
CurrBB.getTerminator()->eraseFromParent();
Builder.SetInsertPoint(&CurrBB);
Value *FCmp = Builder.CreateFCmpOEQ(Call, Call);
Builder.CreateCondBr(FCmp, JoinBB, LibCallBB);
// Add phi operands.
Phi->addIncoming(Call, &CurrBB);
Phi->addIncoming(LibCall, LibCallBB);
BB = JoinBB;
return true;
}
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